Well, one of my shelties coughs and gags and just a single prednil tablet daily stops it, so that is not an expensive fix, but what Hazel suggests would probably make me ask for an x ray. I had a different sheltie(this one's mother) gagging and yes, it was her trachea, and a self inflicted injury because each time I opened the drum to get dry food out for them she would jump and try and get her head down into it. She was hitting her trachea each time, silly girl. Of course I didn't realise what was happening until she got bad.